Behavior-modifying pesticides

Develop models of the dynamics of the baseline ecosystems. (Much of this is already underway via the research programs identified- in 2. Models of pesticide behavior have been developed, but they are based primarily on agricultural uses. They need to be modified and validated for herbicides in the forest.)... 

Currently, the active ingredients and adjuvants of the products used for crop protection in agriculture are nonrenewable (generally of petrochemical origin) and present industrial and environmental risks [79]. The role of surfactants in modifying pesticide behavior has been reviewed on a number of occasions over the past 25 years [References in Ref. 80]. Many published reports have shown that the incorporation of surfactants into pesticide sprays improved efficacy [80]. Since most surfactants used in pesticide formulations are petroleum based, it is conceivable that the growing propensity toward products that are environmentally friendly will work in favor of PBS as potential replacements. 

Many factors affect the mechanisms and kinetics of sorption and transport processes. For instance, differences in the chemical stmcture and properties, ie, ionizahility, solubiUty in water, vapor pressure, and polarity, between pesticides affect their behavior in the environment through effects on sorption and transport processes. Differences in soil properties, ie, pH and percentage of organic carbon and clay contents, and soil conditions, ie, moisture content and landscape position climatic conditions, ie, temperature, precipitation, and radiation and cultural practices, ie, crop and tillage, can all modify the behavior of the pesticide in soils. Persistence of a pesticide in soil is a consequence of a complex interaction of processes. Because the persistence of a pesticide can govern its availabiUty and efficacy for pest control, as weU as its potential for adverse environmental impacts, knowledge of the basic processes is necessary if the benefits of the pesticide ate to be maximized. 

Environmental conditions—residue dissipation. It is well established that environmental conditions modify the behavior of pesticides (38). Long-term worker reentry (5 to 120 days) illnesses have been limited primarily to the hot and dusty central California valley. Since these incidents have been linked to the oxon metabolites and these metabolites reach higher levels in dry areas, rainfall and dew would appear to be additional major components for regionalizing the United States for worker reentry regulations. Davies et (7) proposed such a scheme in 1973. 

Although pesticides continue to be the major approach to boll weevil control, problems related to their use have led to a search for alternative forms of pest control. These Include chemicals that modify behavior and/or development, biological agents, and genetic manipulation. 

It is fully recognized that resistance of insects and mites to insecticides and acaricides can, and frequently does, result from enhanced metabolism by enzymes overexpressed due to insecticide selection pressure. Such metabolic resistance mechanisms are not linked to any specific site of action classification and therefore they may confer cross-resistance to insecticides in more than one IRAC MoA group. Where such metabolic resistance has been characterized and the crossresistance spectrum is known, it is possible that certain alternations, sequences or rotations of MoA groups cannot be used. Similarly, mechanisms of reduced penetration of the pesticide into the pest, or behavioral changes of the pest, may also confer resistance to multiple MoA groups. Where such mechanisms are known to give cross-resistance between MoA groups, the use of insecticides should be modified appropriately. 

Knowledge of plant cuticular components which modify insect behavior will be useful in the control of a given pest. When the component is not a valuable quality factor for consumer acceptance, breeding of plants that lack ovipositional stimulants will reduce pest damage. The use of plant breeding to increase levels of insect ovipositional stimuli could produce plants which will be useful as trap crops. This could lead to the reduction in the use of pesticides which increases production costs and environmental contamination. 

Some papers have dealt with the reversed phase TLC of pesticides. The retention behavior of two pyrolyzed and two chemically modified silicas were investigated in adsorptive and reversed-phase modes in the analysis of triphenylmethane type fungicides and 2-nitro-4-cyanophenyl esters. The modified silicas and the untreated controls were compared (Table 10). The retention parameters of the compounds studied are given for all conditions (132a). 

Certainly, in the case of the insecticides, past experience has shown this approach to be successful, with synthetic pyrethroids as the best example. Other commercially useful botanical pesticides include nicotine, pyrethrum, rotenone and several other alkaloids. Similarly, other natural compounds modifying feeding behavior or inhibiting the growth of insect larvae, are considered viable alternatives to acute toxins, for insect control (3). One of the most successful examples so far is Neem, extracted from the seeds of the tree Azadirachta indica. 

---